西大别地区显著的新元古代岩浆热事件:变花岗岩U-Pb年代学、地球化学及Nd-Hf同位素约束  

The Significant Neoproterozoic Magmatism in the Western Dabie Area, China: Constraints from Zircon U-Pb Age, Elemental and Nd-Hf Isotopic Geochemistry of Meta-granites

作　　者：朱江 陈超[3] 王光洪 吴波[3] 邓新 ZHU Jiang;CHEN Chao;WANG Guang-hong;WU Bo;DENG Xin(College of Resources and Environment,Hubei Key Laboratory of Petroleum Geochemistry and Environment,Yangtze University,Wuhan 430100,China;Wuhan Center,China Geological Survey,Wuhan 430205,China;Hubei Geological Survey y Wuhan 430034,China;No.605 Team of Sichuan Bureau of Metallurgical Geology and Exploration,Meishan Sichuan 620860,China)

机构地区：[1]长江大学资源与环境学院,油气地球化学与环境湖北省重点实验室,武汉430100 [2]中国地质调查局武汉地质调查中心,武汉430205 [3]湖北省地质调查院,武汉430034 [4]四川省冶金地质勘查局605大队,四川眉山620860

出　　处：《矿物岩石地球化学通报》2021年第6期1313-1329,共17页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：湖北省自然科学基金资助项目(2019CFB270);中国地质调查局地质调查项目(DD20190370)。

摘　　要：扬子陆块北缘西大别山地区变质岩系中广泛保留有新元古代岩浆岩,为厘清其原岩成因,对扬子陆块北缘大别区基底性质及新元古代构造-岩浆热事件提供约束,对其中的3处变花岗岩体(五岳山、熊店和方店)的岩石进行了年代学和地球化学分析。结果显示,3处岩体的原岩均为变质程度较低的二长花岗岩,它们的锆石LA-ICP-MS U-Pb年龄分别为(742±2)Ma、(739±3)Ma和(766±4)Ma,与区域红安岩群和定远组双峰式火山沉积建造在时限上具有可对比性。在地球化学组成上,3处花岗岩均具有较高的SiO_(2)(11.72%~15.26%)和总碱(6.40%~8.70%)含量,K_(2)O/Na_(2)O>1;富集轻稀土(La_(N)/Yb_(N)为22.98~28.64),负Eu异常不明显,亏损Ba、Nb、Ta、P、Ti和Y元素;Nd同位素初始比值ε_(Nd)(t)为-15.2~-10.6,t_(DM2)为2.68~2.28 Ga;锆石的Hf同位素初始比值ε_(Hf)(t)为-13.9~-5.1,t_(DM2)为2.32~1.83 Ga。结合岩石矿物组成、地球化学和Nd-Hf同位素分析认为,3处变花岗岩的原岩均可能为(钙碱性)分异的I型花岗岩,系起源于中等深度(压力)条件下的古老地壳物质的重熔。东、西大别地区广泛出露的新元古代中期(780~720 Ma)岩浆岩指示为主动大陆裂谷-拉张伸展背景下构造热事件,可能与Rodinia地幔柱活动有关。The Neoproterozoic magmatic rocks are reserved in metamorphic rocks in the western Dabie area in the northern margin of Yangtze Block.Geochronological and geochemical studies of the Wuyueshan,Xiongdian and Fangdian meta-granites have been carried out,in order to analyze their genesis and to provide constraints on the property of basement and the Neoproterozoic tectonic-magmatic thermal events in the western Dabie area in the northern margin of Yangtze Block.The results show that those meta-granites was formed from the relatively low degree metamorphism of monzongranite.LA-ICP-MS zircon U-Pb dating results reveal that these meta-granites have crystallization ages of(742±2)Ma,(739±3)Ma,and(766±4)Ma,respectively,which are close to ages of the Neoproterozoic bimodal volcanic suites of the Hongan group and Dingyuan formation in the western Dabie area.These meta-granites have relatively high contents of SiO_(2)(11.72%-15.26%)and total alkali(Na_(2)O+K_(2)O is 6.40%-8.70%),with K_(2)O/Na_(2)O>1.They are enriched in LREE(La_(N)/Yb_(N) is 22.98-28.64),with no obvious negative Eu anomaly,and are depleted in Ba,Nb,Ta,P,Ti and Y.Their whole-rock initialε_(Nd)(t)values range from-15.2 to-10.6,with the two-stage Nd model ages(t_(DM2))ranging from 2.68 to 2.28 Ga.Their zirconεHf(t)values vary from-13.9 to-5.1 with two-stage Hf model ages(t_(DM2))varying from 2.32 to 1.83 Ga.Combined with the mineral assemblages,geochemical characteristic,and Nd-Hf isotopes,protoloths of the Wuyueshan,Xiongdian and Fangdian meta-granites belong to the calc-alkaline fractionated I-type granite which could be formed by the partial melting of ancient crustal materials under the medium depth(pressure)condition.We have proposed that the extensively outcropped Neoproterozoic(780-720 Ma)magmatic rocks within the Dabie area are indicatives of tectonic thermal events in the active continental rift-extensional setting which could be associated with the activity of Rodinia plume.

关 键 词：花岗岩 地质年代学 地球化学 Nd-Hf同位素 新元古代 西大别山 

分 类 号：P588.121[天文地球—岩石学]